There are some older threads where people noticed it too, myself included
Would you like to participate in testing of a possible cure workaround for those issues?
Here is the image build off the master with RAM settings tweaked a bit: https://drive.google.com/open?id=1H4K-1sBUttbeHZUaE_J-t-P5cjYiqPU7
If you want to build the image yourself you can use this branch of Armbian build system: https://github.com/armbian/build/tree/nanopi-m4v2-stability-fix
I have mine restarted several times with those settings and I see no crashes on boot/reboot but it certainly needs some longer uptime testing to be deemed successful.